1. Field of the Invention
The present invention relates to random access technology in an orthogonal frequency division multiple access (OFDMA) based cellular system.
2. Description of the Related Art
Resources are shared in wireless communication systems through all resources such as a frequency bandwidth and a transmission time slot being divided into several segments using a multiple access method, for example, time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA), and performing scheduling based on requirements by a user. For more effective use of the resources, a random access method through which all nodes have transmission rights and randomly transmit data may be used by a plurality of nodes as a method of transmitting sporadic data through an uplink common channel.
One random access method includes transmitting a preamble generated using a code randomly selected by a node to a base station and transmitting data for actual random access after receiving a response to the preamble from the base station. In such a method of transmitting the data for the random access, the preamble and the data may be transmitted through a common random access channel and additional resource allocation may be required, irrespective of a random access request by the node.
In a future cellular network, machine-to-machine (M2M) communication may gain an added attention and become further diversified. As the M2M communication applications are further diversified, the number of nodes may drastically increase. Thus, a base station and a network may experience overload that may be caused by a multitude of random access requests from numerous nodes. Hence, an orthogonal frequency division multiple access (OFDMA) based cellular system may need to accommodate a greater number of nodes in a cell and require sufficient random access resources to accept the random access requests from the nodes. In a third generation partnership project (3GPP) long term evolution (LTE) system of the OFDMA based cellular system, the number of preambles used for a conventional random access method is limited to 64. However, when numerous nodes attempt random access with the limited 64 preambles, random access collision probability and random access delay may increase and thus, quality of service (QoS) may not be satisfied. Accordingly, there is a desire for new technology for generating a greater number of preambles with a fixed preamble identification bit number in an existing random access response message and physical random access channels to accommodate a greater number of nodes.